Why Are There Four Cups of Wine at the Seder?

An Exploration in the Talmud Yerushalmi

The Mishnah in Pesahim constructs its Seder around the four cups of wine, and these are a central feature of our Sedarim even today. But why? Why are there any cups at all? Why four? Why doesn't the Mishnah explain this? We'll look at a sugya from the Talmud Yerushalmi—the older, more mysterious cousin of the Talmud Bavli—that discusses this question from several angles, each giving us a window into what the Seder might be about.